PCCSA · Question #6
Match the common TCP/IP protocol with its corresponding port(s).
The options field is empty {}, so I'll explain the concept comprehensively covering all the protocols you'd typically see on this type of exam question. --- TCP/IP Protocol Port Matching Overall Goal Every network service listens on a numbered port so the OS knows which applicati
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Explanation
The options field is empty {}, so I'll explain the concept comprehensively covering all the protocols you'd typically see on this type of exam question.
TCP/IP Protocol Port Matching
Overall Goal
Every network service listens on a numbered port so the OS knows which application should receive incoming packets. Memorizing these is foundational for networking exams (CompTIA Network+, Security+, CCNA, etc.) and real-world firewall/ACL configuration.
Common Protocol-to-Port Mappings
| Protocol | Port(s) | Transport | Purpose |
|---|---|---|---|
| FTP | 20 (data), 21 (control) | TCP | File transfer |
| SSH | 22 | TCP | Encrypted remote shell |
| Telnet | 23 | TCP | Unencrypted remote shell |
| SMTP | 25 | TCP | Send email |
| DNS | 53 | UDP (primarily), TCP | Name resolution |
| DHCP | 67 (server), 68 (client) | UDP | IP address assignment |
| TFTP | 69 | UDP | Trivial (lightweight) file transfer |
| HTTP | 80 | TCP | Unencrypted web traffic |
| POP3 | 110 | TCP | Retrieve email (deletes from server) |
| IMAP | 143 | TCP | Retrieve email (keeps on server) |
| HTTPS | 443 | TCP | Encrypted web traffic (TLS) |
| SMB/CIFS | 445 | TCP | Windows file sharing |
| RDP | 3389 | TCP | Windows remote desktop |
| SNMP | 161 (queries), 162 (traps) | UDP | Network device monitoring |
| LDAP | 389 | TCP/UDP | Directory services |
| LDAPS | 636 | TCP | LDAP over TLS |
| NTP | 123 | UDP | Time synchronization |
Why These Specific Port Numbers?
Most assignments below 1024 are well-known ports standardized by IANA. They aren't arbitrary - they were assigned historically as protocols were formalized. Ports 1024–49151 are registered ports; 49152–65535 are ephemeral/dynamic (used by clients for outbound connections).
What Goes Wrong Without This Knowledge
- Firewalls misconfigured: Blocking port 443 breaks HTTPS; blocking 53 breaks DNS (internet stops working).
- Security gaps: Leaving port 23 (Telnet) open exposes plaintext credentials. Port 22 (SSH) is the secure replacement.
- Troubleshooting failures:
netstat,nmap, and Wireshark output is meaningless if you can't read port numbers.
Memory Tips
| Mnemonic | Ports |
|---|---|
| "FTP splits data/control" | 20/21 |
| "SSH came after Telnet" | 22 > 23 |
| "DNS = 53 (D=4th letter, 4+9=53... just memorize it)" | 53 |
| "HTTP = 80, add S for SSL = 443" | 80 / 443 |
| "RDP = 3389 (3 digits × 3 = remote desktop)" | 3389 |
| "SMTP sends (25), POP3 picks up (110), IMAP inspects (143)" | 25 / 110 / 143 |
The cleanest study method: write each protocol on a flashcard with its port, transport layer (TCP vs UDP), and one-sentence purpose. UDP protocols are typically connectionless, lightweight services (DNS, DHCP, TFTP, SNMP, NTP).
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